The studies proposed are aimed at further investigating in vitro and in vivo the comparative chemosensitivity of metastatic cells versus elements of their original primary experimental tumor and to obtain information on the possible mechanisms of differential sensitivity to anticancer drugs. Investigation will also be conducted to confirm and further analyze the hypothesis that metastases may possess different immunogenicity with respect to the primary tumor and to examine their immunosensitivity and susceptibility to immunological treatments. These studies will exploit tumor sublines of different spontaneous metastasizing capacity and derived from individual metastases which will be characterized as models of metastatization.